Doppler som
- Created by
- Renato Passos, Eng. de Software
- Reviewed by
- Renato Passos, Eng. de Software
Last updated: Apr 18, 2026
About this calculator
The Doppler effect sound calculator determines the perceived frequency (f') when there is relative motion between the sound source and observer. It uses the formula f' = f·(v + v_obs)/(v + v_source), where f is the original frequency, v is the speed of sound in the medium, v_obs is the observer's speed, and v_source is the source's speed. The signs of velocities depend on the direction of motion relative to the observer.
This tool is useful for scenarios like analyzing emergency vehicle sirens in motion, physics experiments, or academic calculations. For example, when a car approaches with its horn on, the sound frequency seems higher to a stationary person. The effect reverses when the source moves away.
Always consider the correct direction of velocity vectors: positive for approaching and negative for receding. The speed of sound (v) depends on the medium (air, 343 m/s at 20°C) and should be adjusted according to the experiment's conditions.
Frequently asked questions
How does the formula change if the source moves relative to the observer?
When the source moves, the source speed (v_source) sign changes in the formula: +v_source if it moves away, -v_source if approaching. A stationary observer keeps v_obs = 0.
Why is the sign different in the formula for a moving observer?
For a moving observer, their speed (v_obs) is added with the correct sign: +v_obs when approaching the source and -v_obs when moving away. A stationary source keeps v_source = 0.
What happens if both the source and observer are moving?
Use the full formula with correct signs: f' = f·(v ± v_obs)/(v ∓ v_source). Positive signs for approaching, negative for receding.
What are real-world applications of the Doppler calculation?
It's used in ambulance sirens, traffic radar, astronomy (stellar motion) and ultrasound (blood flow).